Search results for "Surface Chemistry"
showing 10 items of 721 documents
Über die Stabilität Von Copolymeren aus 1,3,5-Trioxan mit verschiedenen Lactonen
1976
Der thermische Abbau von Copolymeren aus 1,3,5-Trioxan und den Lactonen β-Propiolacton (3-Propanolid), Pivalolacton (2,2-Dimethyl-3-propanolid) und e-Caprolacton (6-Hexanolid) wurde untersucht. Der langsame und vollstandige Abbau der Copolymeren wird zuruckgefuhrt auf 1 eine statistische acidolytische Kettenspaltung durch Carboxyl-Endgruppen, 2 die Abspaltung von Acrylsaure an den sauren Endgruppen, 3 die statistische Kettenspaltung durch Pyrolyse von Esterbindungen vor allem in Sequenzen aus mehreren β-Propiolactonbausteinen. Die Teilreaktionen (1) und (2) konnen durch Zusatz von Butandiol-Diglycidylather-(1,4-Bis(2,3-epoxypropoxy)butan) oder N-(2-Naphthyl)anilin oder von Epoxiden stark ve…
Tail and Head Group Interactions in Phospholipid Monolayers
1996
Abstract The order/disorder transition of the phospholipid 1,2-dihexadecyl-sn-glycero-3-phosphocholine and its derivatives was studied by X-ray reflection and thermodynamic measurements. We find that increasing the length of an ethylene oxide spacer (zero to three EO groups) between the phosphate group and the hydrophobic chains (i) induces a slight shift of the main transition, (ii) reduces the influence of the head groups on the chain lattice, and (iii) increases the head group length and promotes its hydration. For DH(EO)3PC in the ordered phase we find that the small phosphate groups (which are the main source of contrast in X-ray reflectivity) are homogeneously distributed within the h…
Counterintuitive Mechanisms of the Addition of Hydrogen and Simple Olefins to Heavy Group 13 Alkene Analogues
2013
The mechanism of the reaction of olefins and hydrogen with dimetallenes ArMMAr (Ar = aromatic group; M = Al or Ga) was studied by density functional theory calculations and experimental methods. The digallenes, for which the most experimental data are available, are extensively dissociated to gallanediyl monomers, :GaAr, in hydrocarbon solution, but the calculations and experimental data showed also that they react with simple olefins, such as ethylene, as intact ArGaGaAr dimers via stepwise [2 + 2 + 2] cycloadditions due to their considerably lower activation barriers vis-à-vis the gallanediyl monomers, :GaAr. This pathway was preferred over the [2 + 2] cycloaddition of olefin to monomeric…
Isolated Fe(III)-O Sites Catalyze the Hydrogenation of Acetylene in Ethylene Flows under Front-End Industrial Conditions
2018
[EN] The search for simple, earth-abundant, cheap, and nontoxic metal catalysts able to perform industrial hydrogenations is a topic of interest, transversal to many catalytic processes. Here, we show that isolated FeIII¿O sites on solids are able to dissociate and chemoselectively transfer H2 to acetylene in an industrial process. For that, a novel, robust, and highly crystalline metal¿organic framework (MOF), embedding FeIII¿OH2 single sites within its pores, was prepared in multigram scale and used as an efficient catalyst for the hydrogenation of 1% acetylene in ethylene streams under front-end conditions. Cutting-edge X-ray crystallography allowed the resolution of the crystal structur…
Determination of Kinetic and Thermochemical Parameters of a Substitution Reaction at a Square-Planar Palladium(II) Complex in Water/AOT/n-Heptane Mic…
1995
Abstract The substitution reaction [Pd(bipy)(en)] 2+ + en → [Pd(en) 2 ] 2+ + bipy (where bipy = 2,2′-bipyridine and en = ethylenediamine) has been studied in water and water/AOT/ n -heptane microemulsions at various values of the molar ratio R ( R = [water]/[AOT]) by flow microcalorimetry. From calorimetric data, molar enthalpies of reaction and rate constants were obtained. These quantities indicate that, by increasing R , the reaction becomes less exothermic and its rate constant decreases, trending to the value observed in water. These features can be reasonably rationalized in terms of the peculiar solvation state of reactants inside the AOT reversed micelles and/or the peculiar physico…
Self-Assembly of Supramolecular Polymers of N-Centered Triarylamine Trisamides in the Light of Circular Dichroism: Reaching Consensus between Electro…
2020
The self-assembly of chiral supramolecular polymers is an intricate process that spans a wide range of length scales. Circular dichroism techniques are ideal to study this process as they provide information on the molecular scale but are at the same time also sensitive probes of the long-range interactions that control the growth and morphology of these polymers. As yet, Electronic Circular Dichroism that uses electronic transitions as a probe has by far been the method of choice while Vibrational Circular Dichroism, which uses vibrational transitions to probe structure, is much less employed. Here, we report experimental and theoretical studies of the self-assembly of helical supramolecul…
Synthesis of Graphene Nanoribbons by Ambient-Pressure Chemical Vapor Deposition and Device Integration
2016
Graphene nanoribbons (GNRs), quasi-one-dimensional graphene strips, have shown great potential for nanoscale electronics, optoelectronics, and photonics. Atomically precise GNRs can be "bottom-up" synthesized by surface-assisted assembly of molecular building blocks under ultra-high-vacuum conditions. However, large-scale and efficient synthesis of such GNRs at low cost remains a significant challenge. Here we report an efficient "bottom-up" chemical vapor deposition (CVD) process for inexpensive and high-throughput growth of structurally defined GNRs with varying structures under ambient-pressure conditions. The high quality of our CVD-grown GNRs is validated by a combination of different …
Chemical Design and Magnetic Ordering in Thin Layers of 2D Metal–Organic Frameworks (MOFs)
2021
Through rational chemical design, and thanks to the hybrid nature of metal−organic frameworks (MOFs), it is possible to prepare molecule-based 2D magnetic materials stable at ambient conditions. Here, we illustrate the versatility of this approach by changing both the metallic nodes and the ligands in a family of layered MOFs that allows the tuning of their magnetic properties. Specifically, the reaction of benzimidazole-type ligands with different metal centers (MII = Fe, Co, Mn, Zn) in a solventfree synthesis produces a family of crystalline materials, denoted as MUV-1(M), which order antiferromagnetically with critical temperatures that depend on M. Furthermore, the incorporation o…
Features of magnetorheology of biocompatible chain-forming ferrofluids with multi-core magnetic nanoparticles: Experiment and simulation
2020
Abstract We study the magnetorheological properties and structural transitions in novel aqueous colloidal suspensions of magnetic nanoparticles developed for biomedical applications. Defined-shape field-tunable superparamagnetic nanoparticles with clustered cores and their suspensions are produced. The region of intermediate magnetic coupling strength between colloidal ferrofluids and magnetorheological suspensions is systematically studied for the first time. Hybrid numerical simulations with hydrodynamic interactions provide full structural information. The distinctive features of the rheograms are related to transitions between Brownian and persistent microstructure, shape anisotropy, co…
Probing ensemble polymorphism and single aggregate structural heterogeneity in insulin amyloid self-assembly.
2020
Ensembles of protein aggregates are characterized by a nano- and micro-scale heterogeneity of the species. This diversity translates into a variety of effects that protein aggregates may have in biological systems, both in connection to neurodegenerative diseases and immunogenic risk of protein drug products. Moreover, this naturally occurring variety offers unique opportunities in the field of protein-based biomaterials. In the above-mentioned fields, the isolation and structural analysis of the different amyloid types within the same ensemble remain a priority, still representing a significant experimental challenge. Here we address such complexity in the case of insulin for its relevance…